It's no sign of anything that you haven't heard from the CO yet. The case being assigned to him/her just means that the file is now in a date-order queue waiting its turn for his/her attention. That person will be dealing with other people as well as you, so don't think that time passing is down to any difficulties with your case.
Giving a second partner-sponsored work visa is easy, because the checking has already been done for the first visa. INZ already accept that you have a valid partnership, so that hurdle is passed and all is good. However, more paperwork has to be done to put the partner-sponsored Residence application through, and that will take the time that it takes.